Parallel processing continues to be important in large data warehouses as data warehouse demand continues to expand to higher volumes, greater numbers of users, and more applications. Outer joins are frequently generated by Business Intelligence (BI) tools to query data warehouses powered by parallel database management systems (“DBMSs”). Research has been done on some aspects of optimizing outer joins including outer join elimination, outer join reordering and view matching for outer join views. To the inventors' knowledge, little research has been done on outer join optimization in parallel DBMSs, probably because of the assumption that inner join optimization techniques can be largely applied to outer joins as well.